The exp functions compute the value of the exponential function,
    defined as e**x, where e is the constant used as a base for
    natural logarithms.

    The expm1 functions compute exp(x) - 1 accurately, even for tiny
    x.

    If an overflow occurs, the exp functions return the largest
    possible floating-point value and set errno to ERANGE. The
    constant HUGE_VAL is defined in the <math.h> header file to be
    the largest possible floating-point value.